This invention relates to the protection of loudspeakers, and, more particularly, to the protection of loudspeakers against overloading.
It is customary to operate audio amplifiers and their loudspeakers at comparatively high power levels. This produces an acoustical effect which many listeners have likened to that of a live musical source. Unfortunately, the operation of audio equipment at high power levels often damages their speakers.
Such damage usually occurs because the high power levels cause overheating in the voice coils of the speaker. As a result there is either destruction of the wire-to-bobbin bond in the speaker or the creation of a general open circuit that renders the speaker useless. In addition, overheating in the driving equipment can also have a destructive effect on speakers. This is particularly true of semiconductor output devices for which overheating causes short circuits. The speaker is then subjected to high, damaging levels to direct current.
It has been suggested that an overload switch could be included between a loudspeaker and its driver, to operate with a threshold power level is reached beyond which damage could take place. The usual switch is a complex thermal device which often fails or reacts to current overload too slowly particularly in the presence of high levels of direct current. The latter may be present either as components in an audio output signal or by virtue of short circuiting in one of or both drivers. In addition, conventional switches often react only to transients and thereafter restore themselves to their normal condition even though the overloading continues. This results in speaker damage if the overload continues.
Accordingly, it is an object of the invention to facilitate the protection of loudspeakers against overloading. A related object is to avoid overload conditions which could result in speaker damage, for example, by producing an open circuit or by destroying the wire-to-bobbin bond in a speaker.
Another object of the invention is to protect a speaker against overheating in the drive circuitry. A related object is to avoid speaker damage because of short circuiting, for example, of semiconductive devices which result in having the full current level of a power supply appear at the speaker terminals and bring about consequent damage.
A further object of the invention is to simplify overload switch protection. A releated object is a full range of protection with a simple switch. Another related object is to achieve steady state, as well as transient, overload protection.